1. Field of the Invention
The present invention relates generally to a semiconductor device and a manufacturing method therefor, and more particularly, to a semiconductor device having a bonding pad and a manufacturing method therefor.
Related co-pending applications include U.S. Application Ser. No. 146,826 now abandoned, U.S. Application Ser. No. 131,636, and International Application No. PCT/JP87/00555.
2. Description of the Prior Art
FIGS. 1 and 2 are a cross sectional view and a plan view of a bonding pad portion of this kind of conventional semiconductor device, respectively. In FIGS. 1 and 2, a field oxide film (referred to as SiO.sub.2 film hereinafter) 22 is formed on a silicon substrate 21 incorporating circuit elements. A polysilicon (polycrystalline silicon) film 23 and a tungsten silicide film (referred to as WSi film hereinafter) 24 are formed on the SiO.sub.2 film 22 and then, patterned. A silicon dioxide film (referred to as BPSG film hereinafter) 25 containing at least one of phosphorous and arsenic is formed on the WSi film 24. A titanium nitride film (referred to as TiN film hereinafter) 26 and an aluminum film (referred to as Al film hereinafter) 27 are formed on the BPSG film 25 by evaporation or the like.
After the TiN film 26 and the Al film 27 are patterned, an insulating protective film 28 is coated. An opening 28a is formed in a portion of the insulating protective film 28 corresponding to a bonding pad portion of the Al film 27. The Al film 27 thus exposed is used as a bonding pad, so that lead wires (not shown) formed of gold or the like are bonded.
Since the conventional semiconductor device has the foregoing structure, the following problems (1) and (2) exist.
(1) Since adhesion (joining force) between the BPSG film 25 and the TiN film 26 is weak, separation between both the films 25 and 26 is liable to occur at the time of bonding.
(2) Impurities in the BPSG film 25 (particularly, phosphorous or boron) are liable to diffuse into the Al film 27. The impurities cause initial bonding characteristics to be degraded or a gold-aluminum alloy layer to be early deteriorated at a high temperature. As a result, water can enter between the Al film and the lead wire, so that an acid is synthesized, whereby corrosion resistance is deteriorated.
The other prior art includes Japanese Patent Laying-Open Gazette Nos. 9159/1985, 5560/1985 and 57646/1985.
In Japanese Patent Laying-Open Gazette No. 9159/1985, at least one barrier layer formed of refractory metal silicide or nitride is formed in an ohmic contact region on a substrate. An aluminum film is formed on the barrier layer. In Japanese Patent Laying-Open Gazette No. 5560/1985, a barrier layer comprising a double layer of titanium nitride and titanium or a triple layer of titanium, titanium nitride and titanium is provided in a contact portion between metals as a barrier layer for preventing diffusion between the metals. In Japanese Patent Laying-Open Gazette No. 57646/1985, a metal film formed of Ti, Mo, Ta, W or the like or a silicide film thereof is formed under a contact portion or an aluminum interconnection. However, the foregoing prior art is not concerned with the bonding pad.